This invention relates to the production of hydrogen gas from the reaction of aluminum with water in the presence of sodium hydroxide as catalyst.
Hydrogen energy is environment-friendly. Because of the actual human ecology concerns, the exploitation of hydrogen as an universal fuel would be greatly acclaimed. During the last two decades or so, the elaboration of a hydrogen-based economy has made important progress on account of numerous research projects such as the hydrogen fuel cell and the hydrogen car. Although these important discoveries constitute milestones toward a pollution-free society, more research is needed to obtain the hydrogen easily and economically.
A convenient source of hydrogen is a reaction of aluminum with water to split the water molecules into hydrogen and oxygen. The hydrogen is released as a gas and the oxygen combines with the aluminum to form aluminum oxide compounds. Aluminum is the third most abundant element after oxygen and silicon in the earth""s crust, and constitutes approximately 8% by weight of the earth""s crust. Aluminum is a safe material and is commonly used in the food, cosmetics and medical fields. Water is also abundant. Therefore, the reaction of these two elements to produce hydrogen represents an interesting proposal to replace fossil fuels.
Generally speaking, it is known that under certain conditions, aluminum reacts with water to generate hydrogen and heat. It is also known, however, that this type of reaction is not sustainable at ambient temperature. It is believed that a protective oxide layer forms on a metal surface in contact with water at ambient temperature and hinders the reaction. Therefore, it has been accepted by those skilled in the art that the use of aluminum in a reaction with water to generate hydrogen gas requires that the protective oxide layer is efficiently and continuously removed, and that the reaction is kept at an elevated temperature.
A number of hydrogen generators have been developed in the past. The following patent documents constitute a good inventory of the devices and methods of the prior art in the field of hydrogen gas generation using the reaction of aluminum or alloys of aluminum with water.
U.S. Pat. No. 909,536 issued on Jan. 12, 1909, and U.S. Pat. No. 934,036 issued on Sep. 14, 1909, both issued to G. F. Brindley et al. These documents disclose several compositions for generating hydrogen. The compositions comprise any metal which can form an hydroxide when it is brought into contact with a solution of a suitable hydroxide. For example, aluminum is reacted with sodium hydroxide to release hydrogen and to produce sodium aluminate.
U.S. Pat. No. 2,721,789, issued on Oct. 25, 1955 to Q. C. Gill. This document discloses the structure of an hydrogen generator for reacting water with a measured dry charge of aluminum particles and flakes of sodium hydroxide. The reaction releases hydrogen gas and produces sodium aluminate.
U.S. Pat. No. 3,554,707 issued on Jan. 12, 1971 to W. A. Holmes et al. This document discloses a gas generator having bellows to raise or lower the level of water in response to the pressure inside the generator. As the level of water drops, the contact surface between the fuel cartridge and the water is lost and the reaction is terminated.
U.S. Pat. No. 3,957,483 issued on May 18, 1976 to M. Suzuki. This patent discloses a magnesium composition which produces hydrogen upon contact with water. The preferred magnesium composition comprises magnesium, and one or more metals selected from the group consisting of iron, zinc, chromium, aluminum and manganese.
U.S. Pat. No. 3,975,913 issued on Aug. 24, 1976 to D. C. Erickson. This document discloses a hydrogen generator wherein molten aluminum is reacted with water. The generator is kept at a very high temperature to keep the metal in a molten condition.
U.S. Pat. No. 4,643,166 issued on Feb. 17, 1987, and
U.S. Pat. No. 4,730,601 issued on Mar. 15, 1988 both to H. D. Hubele et al. These documents disclose the structure of a fuel cell for producing heat energy and hydrogen gas. The device has a reaction chamber containing a fuel composition that is reactive with water. The fuel composition includes a main fuel part of magnesium and aluminum in a molar ratio of 1:2, and the second part is composed of lithium hydride, magnesium and aluminum in equal molar ratio.
U.S. Pat. No. 4,670,018 issued on Jun. 2, 1987, and
U.S. Pat. No. 4,769,044 issued on Sep. 6, 1988, both to J. H. Cornwell. These documents describe a log made of compressed wood waste and paper. The log is coated with aluminum particles. Upon burning, the aluminum particles react with moisture in the log to emit heat due to the generation of hydrogen gas.
U.S. Pat. No. 4,752,463 issued on Jun. 21, 1988 to K. Nagira et al. This document discloses an alloy which reacts with water for producing hydrogen gas. The alloy material comprises essentially aluminum and 5 to 50% tin.
U.S. Pat. No. 5,143,047 issued on Sep. 1, 1992 to W. W. Lee. This document discloses an apparatus and a method for generating steam and hydrogen gas. In this apparatus, an aluminum or aluminum alloy powder is reacted with water to generate hydrogen gas. An electric power source is used to start the reaction. The electric power source is used to explode an aluminum conductor and to disperse pieces of molten aluminum into a mixture of water and aluminum powder. A heat exchanger is provided to extract useful heat.
U.S. Pat. No. 5,867,978 issued on Feb. 9, 1999 to M. Klanchar et al. This document discloses another hydrogen gas generator using a charge of fuel selected from the group consisting of lithium, alloys of lithium and aluminum. The charge of fuel is molten and mixed with water to generate hydrogen gas.
JP 401,208,30 issued to Mito on Aug. 22, 1989. This document discloses a process for producing hydrogen. Aluminum is reacted with water under an inactive gas or a vacuum to produce hydrogen gas.
CA 2,225,978 published on Jun. 29, 1999 by J. H. Checketts. This patent application discloses a hydrogen generation system wherein a coating on reactive pellets is selectively removed to expose the reactive material to water for producing hydrogen gas on demand. In one embodiment, aluminum and sodium hydroxide are reacted with water to release hydrogen gas and produce sodium aluminate.
DE 3,401,194 published in Jul. 18, 1985 by Werner Schweikert. This document discloses a device for utilizing energy from a chemical reaction between various aluminum alloys and sodium hydroxide. The chemical reaction occurring in this device generates heat, hydrogen gas, a direct current and sodium aluminate as a residue.
FR 2,465,683 published in Mar. 27, 1981 by Guy Ecolasse. This document also discloses a process for producing hydrogen by the reaction of aluminum on sodium hydroxide solution in water. A by-product of this reaction is sodium aluminate.
Belitskus, David. 1970. Technical Note: xe2x80x9cReaction of Aluminum With Sodium Hydroxide Solution as a Source of Hydrogenxe2x80x9d J. Electrochem Soc. (1970), (August), Vol. 117. No. 8, pp.1097-9, XP-002180270. This technical paper.describes several experiments wherein aluminum samples including a cylindrical block, uncompacted powders and pellets of various densities have been reacted with aqueous solutions of sodium hydroxide at various concentrations to generate hydrogen gas. In these experiments, the formation of sodium aluminate was observed, as well as the regeneration of sodium hydroxide through the precipitation of aluminum hydroxide.
Stockburger, D. et al. 1991. xe2x80x9cOn-Line Hydrogen Generation from Aluminum in an Alkaline Solutionxe2x80x9d. Proc.-Electrochem. Soc. (1992), Vol. 92-5 (Proc. Symp. Hydrogen Storage Mater., Batteries, Electrochem., pp. 431-44, 1992, XP-001032928. This technical paper describes three sizes of hydrogen generators in which aluminum is reacted with an aqueous solution of 5.75 M sodium hydroxide. This technical paper also notes the formation of sodium aluminate and the precipitation of aluminum hydroxide that regenerates sodium hydroxide.
Although the chemical reactions of aluminum with water in the presence of sodium hydroxide have been demonstrated in various projects in the past, these reactions were not considered as being safe for use by the general public. Sodium hydroxide is extremely corrosive and must be handled according to particular safety procedures. Therefore, any chemical reaction wherein sodium hydroxide is a consumable would not represent an attractive source of hydrogen for use in vehicles or in household power systems, for examples. As such, it is believed that a need still exists for a method to produce hydrogen gas by the reaction of aluminum and water, wherein the consumables are limited to aluminum and water.
Broadly stated, the process for producing hydrogen gas according to the present invention consists of reacting aluminum with water in the presence of sodium hydroxide acting as a catalyst.
In accordance with one aspect of the present invention, there is provided a process for producing hydrogen gas, comprising the initial step of: providing an aqueous solution in a vessel. The aqueous solution contains sodium hydroxide in a concentration between 0.26 M and 19 M NaOH.
The next step consists of reacting aluminum with water at the surface of the solution thereby generating a region of effervescence at the surface of the solution and a precipitate sinking to the bottom region of the vessel. The process also includes the step of maintaining the region of effervescence separated from the precipitate at the bottom the vessel, to prevent the precipitate from swirling and mixing with the aluminum in the reaction zone at the surface of the solution. This process is advantageous because it proceeds catalytically with the sodium hydroxide acting as the catalyst.
The process mentioned above is best carried out with an aqueous solution containing between about 5M and 10 M NaOH. The process is also more efficient when makeup water is added only after an initial amount of aluminum has been consumed, and when the temperature of the aqueous solution has reached a peak or 75xc2x0 C.
In accordance with another aspect of the present invention, there is provided a process for initiating and maintaining a catalytic reaction of aluminum with water for producing hydrogen gas. The process comprises the initial step of providing an aqueous solution in a vessel. This aqueous solution contains a portion of NaOH and a portion of water. The next steps consist of introducing a portion of aluminum in the aqueous solution, and reacting that portion of aluminum with the portion of water. The process also includes the steps of maintaining constant the portion of NaOH in the vessel and adding additional portions of water and additional portions of aluminum in the vessel according to the rates of consumption of the aluminum and the water in the reaction.
Again, this process is best carried out with an aqueous solution of between 1.2 M and 19 M NaOH and at a temperature between 4xc2x0 C. and 170xc2x0 C.
In yet another aspect of the present invention, there is provided a process for simultaneously producing hydrogen gas and alumina (Al2O3). This process firstly comprises the step of providing an aqueous solution in a vessel. The aqueous solution contains sodium hydroxide in a concentration between 0.26 M and 19 M NaOH. The next step consists of reacting aluminum with water at a surface of the aqueous solution and generating hydrogen gas and alumina. The process also includes the step of recovering hydrogen gas from the surface of the aqueous solution and alumina from a bottom region of the vessel.
Other advantages and novel features of the present invention will become apparent from the following detailed description,.